3 volumes
The Architecture of Human Language
What did this language decide, and who decided differently?
indexed by dimension
Three indexes, one body of facts.
The books are not competing accounts of the same material. Each cuts the same language along a different axis, so a phenomenon shows up once per series with a different question asked of it.
The series
9 volumes
El Árbol
What kind of thing is this, and what else is like it?
indexed by kind
14 volumes
The Reference
How does this language express what I am trying to say?
indexed by primitive
How to read this
The Reference answers the question a learner actually arrives with: how does this language express what I am trying to say. El Árbol answers a structural one: what kind of thing is this, and what else behaves like it. The Architecture of Human Language answers a comparative one: what did this language decide, and who decided differently.
Because the three run in parallel rather than in sequence, a volume is named by its series and its number together. Three different volumes are each numbered 01, and they have nothing to do with one another.